1. Field of the Invention
This invention relates generally to a door apparatus for supporting a door movable relative to a stationary structure between open and closed positions and more particularly to a door apparatus best suited for an automatic door.
2. Prior Art
Long time has elapsed since the mane of "clean room" has been heard and, recently, the clean room has widely been utilized in the field of assembly of precision machine components, in the field of food processing, or in other various fields.
The normal environment in which we live contains a huge number of fine dusts, dirts and fungi adhering thereto. The fine dusts would result in defects or faults in the precision components upon the manufacturing and assembling steps thereof, and would result in decomposition in the food upon the processing thereof. The clean room provides an environment required for the above-described assembling and processing. The clean room is isolated from the outside and is extremely reduced in amount of the fine dusts which would result in the above-described defects or faults and decomposition.
Careful attention is required for a door of a doorway to the clean room in order to prevent the fine dusts from entering the clean room or from being produced within the clean room. Conventional door apparatuses for the clean room will be described with reference to FIGS. 1 and 2. A door 1 is hung by two rollers 2 and 3 from a rail 4 which extends horizontally and is fixedly secured to a wall 5 at a position above a doorway 6 therein such that the door 1 is movable along the rail 4. The rollers 2 and 3 are connected to the door 1 by hanging members 7 and 8, respectively. An upper end of one of the hanging members 7 is fixedly attached to a lower run of a belt 9 trained around a pair of pulleys 11 and 12. The pulley 11 is rotatably mounted on the wall 5 at a position above the rail 4, and the pulley 12 is mounted on an output shaft of a motor 13 for rotation therewith, which is fixedly secured to the wall 5 at a position above the rail 4. The motor 13 is operative in response to a signal from a sensor incorporated in a doormat on a floor, a supersonic or optical sensor disposed adjacent the doorway 6, or the like, to rotate the pulley 12 to thereby move the door 4 connected to the belt 9 between a first position where the door 4 closes the doorway 6 and a second position where the door 4 opens the doorway 6.
Another conventional door apparatus for use at a doorway to the clean room is shown in FIG. 3. A door 21 is driven by a linear motor of a rod type. Spcifically, a rod 22 is fixed to a wall 23 at a location above a doorway 24 therein so as to extend horizontally. A tubular unit 25 for generating traveling or shifting magnetic field is fixedly mounted on a top of the door 21 and is fitted around the rod 22. Annular sliding bearings 26 mounted on the tubular unit 25 enable the same to be smoothly moved along the rod 22 with the door 21 being hung from the rod 22 by the tubular unit 25. When electric current is supplied to the tubular unit 25 through a curled cable 27, the traveling magnetic field is generated between the tubular unit 25 and the rod 22 whereby the tubular unit 25 is moved along the rod 22 and the door 21 is moved between a position where the door 21 closes the doorway 24 and a position where the door 21 opens the doorway 24.
A further conventional door apparatus is known in which a door is hung from a rail by rollers as shown in FIGS. 1 and 2, and is driven by a linear motor of a flat type or by a hydraulic mechanism.
In the above-described conventional door apparatuses, however, the entire weight or load of the door acts on the contact portions such as roller, sliding bearings or the like, and dusts are unavoidably produced at the contact portions. In addition, since the contact portions are located above the door, the fine dusts fall down and the circumference would be contaminated by the fine dusts.